engines). A gas receiver is desirable on the supply side of the throttle. Mufflers are frequently required. They should be much larger than they are commonly built: say 15 times the volume of piston displacement per stroke.
Cost of Gas Power.—The gas engine is essentially more efficient than the steam engine. Generally, a complete gas plant (producers and engines) costs considerably more than a steam plant of the same capacity. Hence the best application of gas power is where fuel costs are high (for both gas and steam) and where the load is steadily maintained. Fixed costs are paid every hour: fuel costs merely during the hours the engine is operated. Incidentally, the question of reliability may sometimes favor steam: steam has also the advantage of lending itself better to heating and process demands.
POWEE COSTS IN A 450-KW. PRODUCER-GAS POWER PLANT (Running on bituminous coal)
. Minimum Normal Maximum
load load load
factor factor factor
Load factor per cent 50 80 100
Output kw -hr. per day 5,000 8,000 10,000
Coal consumption, pounds per kilowatt-hour . . . 2.175 1.940 1.880
Fuel cost cents per kilowatt-hour ............ 0.250 0.223 0.216
Labor cost, cents per kilowatt hour ........... 0.280 0.175 0.140
Supplies and repairs, cents per kilowatt-hour . . . 0.147 0.092 0.074
Total operating cost, cents per kilowatt-hour . . . 0.677 0.490 0.430
Fixed charges, 15 per cent., cents per kilowatt-hr. 0.718 0.449 0.359
Total power cost, cents per kilowatt-hour. . . . 1.395 0.939 0.789
(From MARKS' Mechanical Engineers' Handbook]
The plant of the foregoing table consists of three 150-kw. three-cylinder, vertical Westinghouse, single-acting, four-cycle, engines, with producers. The coal averaged 13,500 B.t.u. per pound and cost $2.30 per short ton delivered. The load is carried 24 hr. daily, 6K days weekly, at a labor cost for two shifts of $14 per day. The cost of the entire plant (producers, engines, generators and auxiliaries) was $180 per kilowatt of capacity.
Classification.—Internal combustion engines using liquid fuel may be two-, cycle or four-cycle. The two-cycle engine compares more favorably with the four-cycle with regard to efficiency than when gas is the fuel, but is nevertheless inferior. Liquid fuel engines may be supplied with a combustible mixture of fuel and air, or the air and fuel may be separately fed. Engines using carburetors belong to the former class. Those of the latter class may receive fuel gradually during the suction and (or) compression strokes, as in many "low pressure" (hot cap or vaporizer) types: or the oil may be injected late in the compression stroke. If compressions exceed 200 lb., the oil must then be forced